Systems and methods for a reducing EMI in a communications switch component utilizing overlapping interfaces

ABSTRACT

A rack-mountable system enclosure for limiting the escape of internally generated electromagnetic interference includes a system case, a front panel, a back panel, overlapped seams formed to couple the front panel and the back panel to the system case such that no gaskets and a minimal number of fasteners including welds, screws and rivets are required, at least one front opening through which communication media passes and apertures formed within the system case for providing air inlet and egress ports.

BACKGROUND

1. Technical Field

The present invention relates generally to rack mountable communicationsystem housings that contain integrated circuitry; and more particularlyto the manner of construct of such communication system housings.

2. Description of the Related Art

Communication systems are well known. Communication systems have existedin many forms for quite some time. For example, the public switchedtelephone network (PSTN) has been in widespread use for many decades.The PSTN is a circuit switched communication network in whichcommunications share time divided bandwidth. Such a circuit switchednetwork is contrasted to the Internet, for example, which is a packetswitched network. In packet switched networks, all communications arepacketized and transmitted in a packetized format from a source to adestination.

Communication systems include a large number of switches coupled bycommunication links. The switches include integrated circuitry thatperforms storage and routing functions for the communications. Thecommunication links may be physical media, e.g., optical fiber, copper,etc. The communication links may also be wireless, e.g., microwavelinks, satellites links, radio links, etc.

As communication demands have been ever increasing, the loads placedupon both the communication switches and the communication links havealso increased. Thus, higher capacity switches and higher capacitycommunication links have been created to meet these demands. With thewide scale miniaturization of integrated circuits, switches can now beconstructed to provide high volume switching but be contained in arelatively small housing. Further, with the development of media such asoptical fiber, the communication links are capable of carryingsignificant levels of communications between switches.

Communication system switches, as is also well known, may be high-speedcarrier network switches that handle a huge amount of traffic or may besmaller switches, which carry lesser volumes of traffic. The amount oftraffic that can be carried by a switch depends upon not only upon thenumber and bandwidth of communication links coupled to the switch butthe processing capabilities of the switch itself. Thus, to increase theprocessing capabilities of the switch, it is important to place allcomponents of the switch into a small area to decrease the size of theswitch.

As switches become ever smaller they experience significant operationalproblems. For example, it is desirable to construct switches such thatthey have a minimum footprint size. Further, it is desirable tomodularize the switches into components. Thus, most switches aretypically constructed to include a plurality of rack mounted switchcomponents/housings, each of which performs a portion of the operationsof the switch. These rack mounted switch components are placedvertically with respect to one another. Each of the switch componentscouples to physical media that forms a communication link and alsocouples to a back plane of the rack so that the switch component mayroute traffic to and from other switch components. This rack-mountedstructure therefore provides great efficiencies in reducing thefootprint size of the overall switch and also allows a number of switchcomponents to be efficiently coupled to one another. Switching functionsmay be divided between the switch components to produce greaterthroughput and for backup/fail over purposes.

However, each switch component produces a large amount of heat becausethe switch component includes a large number of integrated circuits,each of which produces significant heat. Thus, cooling of the integratedcircuits within the switch components is a difficult task. When thistask is not properly accomplished, the integrated circuits on the switchcomponents fail causing the overall capacity of the switch to decreaseand may cause disruption in the communication path that includes theswitch component.

A further difficulty in such a rack mounted switch configuration is thatthe integrated circuits themselves produce electromagnetic interference(EMI). This EMI may be large enough to interfere with other integratedcircuits within the switch components of the rack and even to causedisruption in the back plane coupling the switch components. Further,the Federal Communications Commission limits the amount of EMI energythat may be produced by devices of this type. Thus, it is important toeither design the switch components to minimize EMI or to provideadequate shielding for the switch components.

Each of the switch components physically includes a circuit board uponwhich the plurality of integrated circuits is mounted. Coupled to thisprinted circuit board is a physical media, e.g., optical fiber media.Because of the space limitations for the rack mounted switch components,it is desirable to minimize the overall depth of the switch component.However, in conventional rack mounted switch components, the opticalfiber media is inserted perpendicular to the face of the rack mountedswitch components. This type of mounting increases the depth of theswitch component and often results in unintentional bending of, anddamage to the optical fiber media.

Additional difficulties relate to the structure of printed circuitboards that reside within the switch components. Each switch componenttypically includes at least one circuit board that provides theswitching functionality for the switch component. These circuit boardsfit within a housing that has a predetermined size and that is receivedwithin a rack. Disposed on each circuit board are a plurality ofintegrated circuits, termination points for physical media, and aconnector that couples the circuit board to the back plane of a rack inwhich a respective housing mounts. When any components of the circuitboard fail, the circuit board must be removed from the housing andreplaced with an operational circuit board. During this replacementoperation, the switching functionality of the circuit board is lost.Thus, redundancies are built into the circuit boards, e.g., parallelmedia connection points that couple to parallel media, that cause thecircuit board to provide its functions even when one component fails,e.g., a media coupler. However, such redundancy does not addressproblems caused by the failure of integrated circuits upon the circuitboard. In such case, the circuit board must be fully removed to replacethe circuit board with a fully functioning circuit board.

Traditional Telecom rack assemblies are made to hold rack sub-assemblieshaving a twenty-three inch form factor. Stated differently, the width ofa traditional Telecom sub-assembly is twenty-three inches in width.Lately, however, there is a trend to utilize sub-assemblies having anineteen-inch form factor. Accordingly, vendors of sub-assembliestypically make both nineteen inch and twenty-three inch sub-assemblyproducts according to the requirements of the telecommunication serviceproviders.

From the telecommunication service provider's perspective, it mustdetermine whether to go with a particular nineteen inch or twenty threeinch sub-assembly according to a plurality of considerations includingavailable space for nineteen or twenty three inch racks and, also, thespace within the racks it presently owns or plans to acquire. Thus,logistic issues and space availability considerations may often driveequipment purchase decisions..

Another issue relating that should be considered is that twenty-threeinch sub-assembly systems are traditionally made to conduct exhaust fromcooling air out of a backside of the sub-assembly. Some sub-assemblies,however, are made to conduct exhaust from cooling air out of one of itstwo side panels. Accordingly, a nineteen-inch sub-assembly cannot bemade to merely fit within a twenty-three inch rack without violatingtraditional air exhaust port placement.

These shortcomings, among a great other remain unaddressed by a priorart rack mounted communication system components. Thus, there is a needin the art for improvements in such rack mounted communication systemcomponents.

SUMMARY OF THE INVENTION

The present invention provides a rack mount extension that is formed toconduct cooling air exhaust received from a nineteen-inch sub-assemblyside panel to a rear exhaust port. The rack extension is formed toattach to the sub-assembly and to enable it to be installed into a rackhaving a twenty-three inch form factor. The rack-mountable systemfurther forms an enclosure for limiting the escape of internallygenerated electromagnetic interference and includes a system case, afront panel, a back panel, overlapped seams formed to couple the frontpanel and the back panel to the system case such that no gaskets and aminimal number of fasteners arc required, and at least one front openingthrough which communication media passes and apertures formed within thesystem case for providing air inlet and egress ports. The systemenclosure further defines a first volume that receives a cooling fanmodule, a second volume that receives a plurality of integrated circuitboards, and a third volume through which cooling air exits.

Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a schematic view of a rack-mounted-switch that includes aplurality of rack-mounted switch components constructed according to thepresent invention;

FIG. 2 is a perspective view of a rack-mounted switch componentconstructed according to the present invention that has been removedfrom the rack of FIG. 1;

FIG. 3 is an exploded view of the rack-mounted switch component of FIG.2;

FIG. 4 is a sectional view of a seam of the enclosure of therack-mounted switch component of FIG. 2;

FIG. 5 is a sectional view of one embodiment of an enclosure of therack-mounted switch component, of FIG. 2 constructed according to thepresent invention;

FIG. 6 is a sectional view of a second embodiment of an enclosure of therack-mounted switch component of FIG. 2 constructed according to thepresent invention;

FIG. 7 is a perspective view illustrating the construction of a portionof a multi-fan module of the present invention that assists inpreventing EMI leakage from the enclosure;

FIG. 8 is a schematic view of a motherboard and two daughter boardsconstructed according to the present invention;

FIG. 9 is a schematic view illustrating the relative positioning of themulti-fan module, the motherboard and daughter boards of the presentinvention;

FIG. 10A is a diagrammatic sectional view showing the construction ofcard guides, according to the present invention, that causes a divertedairflow;

FIG. 10B is a diagrammatic sectional view of a card guide constructedaccording to the present invention;

FIGS. 11A and 11B are schematic views illustrating a motherboard and adaughter board with a reset switch constructed according to the presentinvention that may be employed to reset the components of a motherboard;

FIG. 12 is a schematic view illustrating the structure of motherboardand daughter board extractors constructed according to the presentinvention;

FIG. 13 is a schematic view illustrating daughter boards that areengaged within a motherboard according to the present invention;

FIG. 14 is a schematic view of the motherboard with one daughter boardremoved therefrom illustrating the manner in which the daughter boardengages the motherboard;

FIG. 15A is a perspective cutaway view of a nineteen-inch sub-assemblywith an attached four-inch rack-mount extension formed to conductexhaust from a rear side according to one embodiment of the presentinvention;

FIG. 15B is a perspective view of a four-inch rack-mount extensionillustrating air inlet and exhaust ports;

FIG. 15C is a perspective view of a four-inch rack-mount extensionillustrating the closed sides having a plurality of embossments forreceiving mounting hardware and further illustrating that the extensionis formed to also be a duct for exhaust air according to one embodimentof the described embodiment;

FIG. 16 is a perspective view of a fan tray formed to receive and hold aplurality of fans for cooling a sub-assembly;

FIG. 17 is a schematic view of a multi-fan module constructed accordingto the present invention;

FIG. 18 is a schematic view of a fan constructed according to thepresent invention;

FIG. 19 is a schematic top, view of a multi-fan module constructedaccording to the present invention with fans partially removedtherefrom;

FIG. 20 is a schematic side view of a multi-fan module constructedaccording to the present invention;

FIG. 21 is a schematic view of a prior art technique for couplingoptical fiber media to a printed circuit board;

FIG. 22 is a schematic view of a daughter board constructed according tothe present invention in which optical fiber media couples to thedaughter board substantially parallel to a front edge of the daughterboard;

FIG. 23 is another view of a daughter board constructed according to thepresent invention showing the manner in which optical fiber mediacouples to the daughter board;

FIG. 24 is a diagrammatic top view of a daughter board constructedaccording to the present invention showing the manner in which opticalfiber media couples to the daughter board;

FIG. 25 is a logic diagram illustrating a method for inserting a faninto the multi-fan tray according to the present invention;

FIG. 26 is a logic diagram illustrating a method installing an opticalfiber media onto a printed circuit board according to the presentinvention; and

FIG. 27 is a logic diagram illustrating a method for constructing a cardguide according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a rack-mounted switch 100 that includes aplurality of rack-mounted switch components 102A through 102Iconstructed according to the present invention. Each of the 19-inchrack-mounted switch components must fit within a space having a maximumdimension of 17.72 inches wide, 12 inches deep and 1-¾ inches in height.These dimensions are substantially standardized within the industriesfor rack-mountable communications and for other communication systemrack-mounted equipment. Thus, each rack-mounted switch componentincludes a housing that contains the other parts of the rack-mountedswitch components and, at the same time, conforms to the sizelimitations.

The rack includes side supports 106 to which the switch components102A-102I attach. Further, the rack also includes back plane connectionsto allow the switch components 102A-102I to communicatively intercouplewith one another. Such a rack structure is generally known in the artand will not be described further herein except as to expand upon theprinciples of the present invention.

As is shown, physical media 104A-104I extends switch components102A-102I, respectively. According to one embodiment of the enclosure ofthe present invention, the physical media 104A-104I are optical fibermedia that exit the enclosure in a direction substantially parallel to afront surface of the switch components 102A-102I housings. By having themedia extend in such a direction, with respect to the switch components102A-102I housings and the rack 100 in which the switch components102A-102I mount, a lesser depth for the combination of the switchcomponents 102A-102I and the physical media 104A-104I results. Ininstallations in which floor space and access space is limited, thisreduction in depth greatly simplifies the installation of the rack 100.

FIG. 2 is a perspective view of a rack-mounted switch componentaccording to the present invention that has been removed from the rackof FIG. 1. An external portion of the rack-mounted switch component isreferred to as an “enclosure” 200. The enclosure 200 is formed of metaland substantially surrounds all components contained therein. As will bedescribed further with respect to FIG. 3 and subsequent figures,contained within the enclosure 200 are circuit boards, which contain aplurality of integrated circuits, interconnections for the circuitboard, cooling fan structure and connection structures for the physicalmedia.

The enclosure 200 includes a metal shell 202 that is formed from aplurality of pieces. The manner in which the metal shell of theenclosure is formed will be described further with reference to FIGS. 4,5 and 6. The enclosure 200 also includes rack-mounting brackets 204A and204B for securing the enclosure 200 within the rack as was illustratedin FIG. 1.

FIG. 3 is an exploded view of the rack-mounted switch component of FIG.2. As is shown, a rack-mounted switch component 300 includes anenclosure having a system case that includes a first portion 302A and asecond portion 302B. The enclosure also includes a front panel 304 and aback panel 306. Contained within the enclosure are a multi-fan module308, a first motherboard/daughter board combination 310, and a secondmotherboard/daughter board combination 312. The motherboard and daughterboard combinations 310 and 312 are received within the enclosure duringnormal operation. The back panel 306 of the enclosure includes a backplane connector 314 to which the motherboard/daughter board combinations310 and 312 connect.

FIG. 4 is a sectional view of a seam of the enclosure of therack-mounted switch component of FIG. 2. As shown in FIG. 4, anoverlapping seam 402 joins two metal sections 404 and 406 of theenclosure. These two metal sections 404 and 406 may be two of the systemcase and the front panel, the system case and the back panel, or anyother two components of the enclosure. As is shown, this overlappingseam structure 402 eliminates a line of sight from within the enclosureexternal to the enclosure. Therefore, the seam 402 prevents internallygenerated electromagnetic radiation interference (EMI) from escaping theenclosure along the seam 402. As is generally known, integrated circuitsoperating at high switching frequencies generate EMI energy. If this EMIenergy escapes the enclosure, it would be EMI that would interfere withoperation of other integrated circuits. Thus, the seam structure 402illustrated in FIG. 4 provides significant shielding for thosecomponents contained within the enclosure and also prevents thosecomponents within the enclosure from causing interference with othercomponents external to the enclosure.

An additional benefit of the seam structure 402 of FIG. 4 is that itallows the enclosures of the present invention to be constructed withminimal welding. As is generally known, in forming EMI shieldedenclosures of metal, it is typical to weld each and every seam of theenclosure fully along the length of the seam. This welding is expensiveand delays the construction of the enclosures. The seam 402, as shown inFIG. 4, allows enclosures to be constructed with minimal spot welds,screws, rivets or fasteners or the equivalent (collectively “fasteners”)while still providing superior EMI shielding.

FIG. 5 is a sectional view of one embodiment of an enclosure 500 of therack-mounted switch component of FIG. 2 constructed according to thepresent invention. The enclosure is constructed to include threevolumes. A first volume 502 is constructed to accept a multi-fan module.The multi-fan module produces an airflow that passes across the surfacesof two motherboard/daughter board combinations that are received withina second volume 504 of the enclosure. A third volume 506 serves as aplenum area to allow air that has been heated, via passing across themotherboard/daughter board combinations, to exit the enclosure.

In this embodiment, the system case is formed of a first portion 508 anda second portion 510 that are joined using the joints 402 illustrated inFIG. 4. The first portion 508 and second portion 510 of the system casedefine the third volume 506. Another component 512 of the enclosureserves to segregate the first volume 502 from the second volume 504. Thecomponent 512 also provides support for a pair of tracks 514 and 516that will act as the card guides of the motherboard/daughter boardcombinations 310 and 312 (of FIG. 3). The structure 512 is perforated toallow air created by the multi-fan modules to pass from the first volume502 into the second volume 504 that receives the motherboard/daughterboard combinations. The first portion 510 of the system case alsoincludes a component 522 that segregates the second volume 504 from thethird volume 506. This component 522 supports a pair of tracks 518 and520 that will receive card guides of the motherboard/daughter boardcombinations. This component 522 of the first portion 510 of the systemcase also includes perforations that allow heated cooling air to passfrom the second volume 504 to the third volume 506. This heated air isvented from the third volume 506 to exit the enclosure of the systemcomponent. Thus, as with the structure of FIG. 5, the enclosure may beconstructed fairly simply from pre-formed metal sheeting with minimalwelds or equivalent fasteners required and provide significant EMIshielding.

FIG. 6 is a sectional view of a second embodiment of an enclosure of therack-mounted switch component of FIG. 2 constructed according to thepresent invention. The second embodiment of the enclosure includes afirst volume 602 for receiving a multi-fan module, a second volume 604for receiving the pair of motherboard/daughter board combinations, and athird volume 606 that serves as a plenum. The system case includes twocomponents 608 and 610 that are preformed of metal. These components 608and 610 are joined, via the joint structure 402 of FIG. 4, to providesuperior EMI shielding. Component 610 also includes tracks 612, 614, 616and 618 that receive the motherboard/daughter board combinations withinvolume 604. Perforated portions 620 and 622 of component 610 allowcooling air to flow from the first volume 602 to the second volume 604,and from the second volume 604 to the third volume 606, respectively.

FIG. 7 is a perspective view illustrating the construction of a portionof a multi-fan module of the present invention that assists inpreventing EMI leakage from the enclosure. The multi-fan module resideswithin the first volume (e.g., the first volume 502 of FIG. 5 and thefirst volume 602 of FIG. 6) of a housing that is constructed to minimizeEMI leakage. Because the multi-fan module must have a substantiallyuninhibited opening external to the enclosure so that it may receivecool air for cooling the motherboard/daughter board combinations, itmust avoid having a line of sight path external to the enclosure. Thus,the structure of this portion of the multi-fan module includes a frontpanel 702, a top panel 704, and a bottom panel 706. Also included is anopening 708 that allows air to be drawn into the multi-fan module fromexternal in to the enclosure. An inner panel 718 joins top panel 704 andbottom panel 706 and helps prevent EMI leakage through opening 708.

Curved surfaces 710 and 712 formed in bottom panel 706 and top panel704, respectively, serve to reduce/preclude EMI leakage through opening708. In particular, curved surfaces 710 and 712, in combination withfront panel 702 and inner panel 714, provide a trapping mechanism forinternally produced EMI. Thus, free airflow may pass through opening 708and along a surface 718 of panel 714 into the multi-fan module forcooling the motherboard/daughter board combinations.

FIG. 8 is a schematic view of a motherboard and two daughter boardsconstructed according to the present invention. As shown in FIG. 8, amotherboard/daughter board combination 800 includes a motherboard 802, adaughter board 804, and a daughter board 806. Contained upon bothsurfaces of motherboard 802 are integrated circuits. These integratedcircuits may be mounted to motherboard 802 via hole connections orsurface mount connections. The manner in which integrated circuits areaffixed to circuit boards is generally known and will not be discussedfurther herein except as to expand upon the teachings of the presentinvention.

Integrated circuit components and media connectors are affixed to bothsurfaces of daughter boards 804 and 806. The structure of circuit boardsthat include media connectors and integrated circuits is also known andwill not be described further except as to expand upon the teachings ofthe present invention. Fixed to the motherboard 802 is a pair of cardguides 808 and 810. These card guides 808 and 810 matingly engage a pairof tracks (e.g., tracks 612 and 616 of FIG. 6) contained within anenclosure. With the motherboard fully engaged within the enclosure, aback plane connector 812 fixed to the motherboard 802 couples to a backplane connector contained within the enclosure. In this fashion, themotherboard 802 may communicate with other devices coupled to the backplane connector of a rack in which the enclosure mounts via the backplane connector of the enclosure.

Each of the daughter boards 804 and 806 matingly engages with themotherboard 802 via connectors. For example, daughter board 804 includesa connector 818, which engages a connector 816 of motherboard 802.Likewise, daughter board 806 includes a connector 820, which engages aconnector 814 of motherboard 802. The manner in which the daughterboards 804 and 806 couple to the motherboard 802 is in a co-planerfashion. In this co-planer fashion, daughter boards 804 and 806 residein substantially the same plane as the motherboard 802. By having thisco-planer connection, the daughter boards 804 and 806 may be removedfrom the motherboard 802 without removing the motherboard 802 from theenclosure. This provides significant benefits in replacing daughterboards that have failed components without disabling the operation ofthe motherboard. For example, in one embodiment, daughter boards 804 and806 provide redundancy in communication paths provided by coupled media.If one of the daughter boards fails, e.g., daughter board 804, thefailed daughter board 804 may be separated from the motherboard 802without disabling the other daughter board 806 or the motherboard 802.

To support this co-planer functionality, the latching mechanism withwhich the daughter boards 804 and 806 couple to the motherboard 802 andthe manner in which the motherboard 802 couples to the enclosure is asignificant improvement over prior devices. The latching structure thatlatches the motherboard 802 to the enclosure includes a first extractor822 and a second extractor 824. These extractors 822 and 824 couple tothe card guides 808 and 810, respectively, and may only be disengagedfrom the enclosure when the daughter boards 804 and 806 are disengagedfrom the motherboard 802. Extractors 828 and 830 couple the daughterboard 806 to the motherboard 802. Further, extractors 832 and 834 couplethe daughter board 804 to the motherboard 802. Extractors 828 and 834are constructed to be coexistent with extractors 822 and 824,respectively.

FIG. 9 is a schematic view illustrating the relative positioning of themulti-fan module, the motherboard and daughter boards of the presentinvention. As shown in FIG. 9, a multi-fan module 900 resides adjacent amotherboard 902. Connected to motherboard 902 are daughter boards 904and 906. As was previously described, the multi-fan module 900 producesan airflow that is directed across the upper and lower surfaces of themotherboard 902 and the upper and lower surfaces of daughter boards 904and 906 to cool the integrated circuit components disposed thereon. FIG.9 also shows faceplates 908 and 910 disposed upon daughter boards 904and 906, respectively. These faceplates 908 and 910 assist in preventingEMI produced by the components of motherboard 902 and daughter boards904 and 906 from escaping the enclosure.

FIG. 10A is a diagrammatic sectional view showing the construction ofcard guides according to the present invention that causes a divertedairflow. As shown in FIG. 10, the multi-fan module produces an airflow1002 that passes through a dividing wall 1004 having airflow openingsthereupon. The airflow 1002 enters a second volume of the enclosure inwhich motherboards 1010 and 1012 (and coupled daughter boards) arecontained. Fixed to the dividing wall 1004 are tracks 1014 and 1016 thatreceive card guides 1014 and 1016.

Contained upon the motherboards 1010 and 1012 are integrated circuits(ICs). These integrated circuits are contained on both surfaces of themotherboards 1010 and 1012. As is known, integrated circuit componentsgenerate substantial amounts of heat that must be removed from theintegrated circuits to prevent the integrated circuits from over-heatingand failing. Thus, the airflow 1012 passes across the surfaces of themotherboards 1010 and 1012 to remove the heat generated by theintegrated circuits. According to the present invention, card guides1014 and 1016 are designed to control the volume of airflow 1002 so thatit advantageously and effectively cools all integrated circuitscontained upon the motherboards 1010 and 1012.

FIG. 10B is a diagrammatic sectional view of a card guide constructedaccording to the present invention. Referring now to FIG. 10B, theelongated-guide includes a first portion 1050 that slidingly engages thetrack 1008 and a second, portion 1052 that is affixed to the motherboard1010. As is shown, the second portion 1052 of the elongated guide 1014is offset from the first portion 1050 of the elongated guide. Suchoffset of the first portion 1050 to the second portion 1052 alters theairflow 1002 applied to a bottom surface of the circuit board 1054 andto a top surface 1056 of the motherboard 1010. The structure of theelongated guides 1014 and 1016 are designed to correctly divertappropriate portions of the airflow 1002 to the various surfaces of themotherboards 1010 and 1012.

Referring again to FIG. 10A, the second volume within the enclosureoccupied by the motherboards/daughter boards 1010 and 1012, may besubdivided into 3 particular sub volumes. A distance 1018, that is, thedistance between the top inner surface of the enclosure 1000 and anupper surface of motherboard 1010, corresponds to a first sub volume1030. A second distance 1020 is the distance between a lower surface ofthe upper motherboard 1010 and an upper surface of the lower motherboard1012 and corresponds to a second sub volume 1032. A third distance,distance 1022, is the distance between an inner surface of the lowerside of the enclosure 1000 and the lower surface of motherboard 1012 andcorresponds to a third sub volume 1034.

According to the present invention, integrated circuitry is laid out onboth sides of the motherboards 1010 and 1012. Further, integratedcircuitry is also laid out on daughter boards that couple to themotherboards. These daughter boards are not shown in the sectional viewof FIG. 10A but their structure will be apparent to the reader fromviewing the other drawings. Each of the integrated circuits contained onthe surfaces of the motherboards 1010 and 1012, as well as the daughterboards, generates heat. Because the motherboards 1010 and 1012, as wellas the daughter boards, are good thermal insulators, the heat generatedin each of the sub volumes 1030, 1032 and 1034 must be removed in adirection parallel to the surfaces of the motherboards 1012 and 1010.Since the total cooling provided by the airflow 1002 is known, the cardguides 1014 and 1016 have offsets to divert airflow based upon the heatthat is generated within each of the volumes 1030, 1032, and 1034.

Given that a particular airflow volume 1002 is sufficient to cool allintegrated circuits contained within sub volumes 1030, 1032, and 1034,the offsets are determined to produce optimum cooling. Integratedcircuits that are more temperature sensitive, i.e., that cannot beoperated at higher temperatures, are placed on the motherboards 1010,1012 and the daughter boards to be closer to the multi-fan module suchthat they receive a larger cooling airflow. Further, integrated circuitsthat produce higher levels of heat and/or are less temperature sensitivemay be placed on portions of the motherboards 1010 and 1012 farther fromthe multi-fan module.

FIGS. 11A and 11B are schematic views illustrating a motherboard and adaughter board with a reset switch constructed according to the presentinvention that may be employed to reset the components of a motherboard.A motherboard 1100 couples to daughter boards 1102 and 1104. However,the components of the motherboard 1100 are not accessible directlywithout removing the daughter boards 1102 and 1104 from the motherboard1100. Thus, a card guide 1108 includes a reset switch 1110 that moveswithin the card guide 1108 and couples to a reset device 1106. Thisreset device 1106, when activated via the reset switch 1110, causes themotherboard 1100 to enter a reset mode. Thus, when the motherboard 1100enters an inoperative state, it may be reset without removing daughterboards 1102 and 1104 from the motherboard 1100 and from the housing.

FIG. 12 is a schematic view illustrating the structure of motherboardand daughter board extractors constructed according to the presentinvention. As shown in FIG. 12, a daughter board 1202 includesextractors 1204 and 1206. Extractor 1204 engages an extraction surfacefixed to the daughter board 1202. A motherboard extractor 1210 pivotallyattaches to a first portion 1212 of a card guide 1216 and engages theenclosure (not shown). Further, extractor 1206 engages an extractionsurface 1208 fixed to a second portion 1214 of the card guide 1216.

In the illustrated embodiments each of the extractors 1204 and 1206, andmotherboard extractor 1210 includes an actuator and an extractionsurface. A person uses respective actuators to move the extractors 1204and 1206, and motherboard extractor 1210 between engaged positions andreleased positions. However, it may be advantageous to further preventunintentional actuation of the motherboard extractor 1210. Thus, inanother embodiment, the motherboard extractor 1210 does not include anactuator that may be grasped, but, instead, includes a slot thatreceives a screwdriver or a similar tool, with such tool required tomove the motherboard extractor 1210 from an engaged position to areleased position. In this fashion, the motherboard extractor 1210cannot be disengaged from the enclosure without the use of a tool. As isevident, the use of extractors 1204 and 1206 allow the daughter board1202 to be disengaged from a motherboard 1220.

FIG. 13 is a schematic view illustrating daughter boards that areengaged within a motherboard according to the present invention. Theview of FIG. 13 shows a motherboard 1300 with which daughter boards 1302and 1304 are matingly engaged. Extractors 1306 and 1308 are used toengage and remove the motherboard 1300 from an enclosure. Extractor 1306is shown in an engaged position even though the motherboard 1300 isremoved from the enclosure. Extractors 1306 and 1308 are shown in areleased position.

Daughter board 1302 includes extractors 1310 and 1312. Daughter board1304 includes extractors 1314 and 1316. Each of the extractors 1310,1312, 1314, and 1316 is in the engaged position. As is shown, thedaughter board extractors 1310, 1312, 1314, and 1316 are in the engagedposition and their front edges are flush with the front edge ofmotherboard 1300, as well as with the front edge of motherboardextractor 1306 that is in the engaged position. Further, the extractorsin the engaged position are also flush with faceplates 1320 and 1322 ofdaughter boards 1302 and 1304, respectively. The flush alignment of eachof these components not only reduces the depth of the combination of themotherboard 1300 and daughter boards 1302 and 1304, but also assists inpreventing EMI generated by the motherboard 1300 and daughter boards1302 and 1304 from escaping from an enclosure in which these componentsare contained.

FIG. 14 is a schematic view of the motherboard with one daughter boardremoved therefrom illustrating the manner in which the daughter boardengages the motherboard. As shown in FIG. 14, a motherboard 1300 and adaughter board 1302 are matingly engaged. In this engaged position,daughter board extractors 1310 and 1312 are in their engaged positionsengaging extraction surfaces 1402 and 1404, respectively. As waspreviously described, extraction surface 1402 is fixed to the secondportion of the elongated guide. However, extraction surface 1404 isfixed to a daughter board track 1406, which, in turn, is fixed tomotherboard 1300. As is also shown in FIG. 14, extraction surface 1408is also affixed to the daughter board track 1406. The other daughterboard 1304 (not shown) uses this extraction surface 1408 when matinglyengaging the motherboard 1300.

FIG. 15A is a perspective cutaway view of a nineteen-inch sub-assemblywith an attached four-inch rack-mount extension formed to conductexhaust from a rear side according to one embodiment of the presentinvention. As may be seen, a sub-assembly seen generally at 1500 isattached to a four-inch rack-mount extension shown generally at 1504. Atan end opposite of the extension 1504, sub-assembly 1500 includes anarea 1508 for receiving a fan tray.

A front side of sub-assembly 1500 includes an inlet port shown generallyat 1512 for receiving air that is propelled through the sub-assembly1500 by the fans of a fan tray once a fan tray is installed. As may alsobe seen, extension 1504 includes a bracket 1516 that is attached theretoto enable sub-assembly 1500 to be mounted within a rack having atwenty-three inch form factor.

In operation, the fans of the fan tray draw air into the sub-assembly1500 in direction 1520 through inlet port 1512. The air drawn in throughinlet port 1512 is then propelled in a generally axial direction showngenerally at 1524. The air is exhausted from sub-assembly 1500 throughat least one exhaust port 1528. The extension 1504 then receives theexhaust through an inlet port shown generally at 1532 and conducts theair towards a rear exhaust port 1534 of the extension 1504 as is shownat 1536. The exhaust air is then expelled from the extension 1504 in adirection 1540 through extension 1504 rear exhaust port 1534. As may beseen in this diagram and with a comparison of the arrangement of thefiber optic couplers, the fiber optic couplers, when installed, areaxially aligned with the airflow within the sub-assembly 1500 in axialdirection 1524. Moreover, a “front door” shown generally at 1544 isshown from which fiber optic fibers extend from the sub-assembly 1500.

In the described embodiment of the invention, the sub-assembly 1500 isformed of 18-gauge metal (0.048 inches thick) while the extension 1504is formed of 16-gauge metal (0.060 inches thick). Additionally,extension 1504 forms openings sufficiently large enough to enable atightening tool, such as an Allen wrench or a screwdriver, to beinserted therein to tighten screws that are used to firmly secure theextension to the sub-assembly 1500. Here, in the described embodiment,#8 captive screws with 32 threads per inch are used because they serveto easily and firmly attach the extension 1504 to the sub-assembly 1500.Alternate screws and methods for attaching the extension 1504 may alsobe used. One reason the extension 1504 is formed of 16-gauge steel is toprovide adequate strength of the extension put in a high shock andvibration environment.

FIG. 15B is a perspective view of a four-inch rack-mount extensionillustrating air inlet and exhaust ports. In the described embodiment ofthe invention, extension 1504 includes substantially closed top, bottomand sides, except for screw holes and air inlet and exhaust ports.Accordingly, extension 1504 is formed to not only be an extension toenable a nineteen-inch sub-assembly to be inserted into a rack having atwenty-three-inch form factor, but is also formed to be a duct to directexhaust air that is expelled from a side of a sub-assembly towards arear of a rack.

Sub-assembly extension 1504 forms an air inlet, shown generally at 1548,for receiving exhaust air from the sub-assembly and an air exhaust port,shown generally at 1552, through which exhaust air is expelled. As mayalso be seen, extension 1504 forms a plurality of mounting flanges 1556for attaching the extension 1504 to a sub-assembly. Finally, a pluralityof apertures 1560 through which a tightening tool, such as a screwdriveror Allen wrench, may be inserted to tighten captive panel screws thatare attached at the apertures shown at 1564. While some exhaust air willescape from the apertures 1560 of extension 1504 for the tighteningtool, most of the exhaust air will be expelled through exhaust port1552.

FIG. 15C is a perspective view of a four-inch rack-mount extensionillustrating the closed sides having a plurality of embossments forreceiving mounting hardware and further illustrating that the extensionis formed to also be a duct for exhaust air according to one embodimentof the described embodiment. Extension 1504 includes a closed end 1568and a substantially closed side 1570. Substantially closed side 1570includes apertures 1560 for receiving a tightening tool. Substantiallyclosed side 1570 further includes a plurality of embossments showngenerally at 1572 for receiving mounting hardware for attaching asub-assembly 1500 with extension 1504 to a rack with a twenty-three-inchform factor. Embossments 1572 are formed to mate with and receive themounting hardware 1516 of FIG. 15A.

FIG. 16 is a perspective view of a fan tray formed to receive and hold aplurality of fans for cooling a sub-assembly. Fan tray 1600 includes aninlet port 1602 that is similar to inlet port 1512 of FIG. 15A. Aplurality of removable fans shown generally at 1604 is formed to havesupport flanges 1608 formed at the inlet and exhaust ends of theremovable fans 1604. Support flanges 1608 are formed to providestructural rigidity to the fan and to be large enough to form mountingsurfaces that are used to attach the fan to the fan tray 1600. In thedescribed embodiment, support flanges 1608 further form apertures 1612through which a mounting screw may be inserted. Additionally, in thedescribed embodiment of the invention, support flanges 1608 are alsoformed to facilitate being riveted to the fan tray 1600 in the areagenerally formed at 1616. As may be seen, fan tray 1600 is formed toreceive six fans. In addition to the two fans 1604 shown in FIG. 16,four fan-receiving stations 1620 are shown. Each of the installed fansreceives inlet air that enters the fan tray through inlet port 1602 andexpels the air in direction 1624 to cool circuit components of thesub-assembly.

FIG. 17 is a schematic view of a multi-fan module constructed accordingto the present invention. The multi-fan module 1700 includes a pluralityof fans 1702A through 1702E. The multi-fan module 1700 includes a frontedge 1704 that has a plurality of front airflow apertures 1706A through1706E. The plurality of fans 1702A through 1702E receive air via thefront airflow apertures 1706A through 1706E. The multi-fan module alsoincludes a bottom surface 1708 that vertically limits the engagedposition of the plurality of fans 1706A through 1706E a and a backsurface 1710 that includes a plurality of back airflow apertures.

The multi-fan module 1700 also includes a top surface 1712 thatcooperates with the enclosure to provide an air plenum opening throughwhich air is received into the fans 1702A through 1702E. According tothe operation of the multi-fan module 1700, air is received through theplurality of front airflow apertures 1706A through 1706E and producedfrom the back airflow apertures (not shown). The back airflow aperturesreside adjacent the enclosure volume within which themotherboard/daughter board combinations reside.

FIG. 18 is a schematic view of a fan constructed according to thepresent invention. A fan 1800 includes a fan motor 1802, a plurality offan blades 1804 coupled to the fan motor 1802, and a fan housing 1806that houses the fan motor 1802 and the plurality of fan blades 1804. Thefan 1800 also includes wiring 1808, which is attached to an externalpower source to power the fan motor 1802. The fan housing 1806 includesa flange 1810 located at one end of the fan housing 1806. This flange18,10 is received by fingers formed in the front edge of the multi-fanmodule to hold the fan 1800 in place within the multi-fan module.

FIG. 19 is a schematic top view of a multi-fan module constructedaccording to the present invention with, fans partially removedtherefrom. As shown in FIG. 19, the multi-fan module 1900 includes a topsurface 1904, a front edge 1908, and a back surface 1912. As is shown,front airflow apertures 1916A and 1916B (as well as the other frontairflow apertures) includes 2 fingers for holding the flange of a fanmotor. In particular, front airflow aperture 1916A includes fingers 1918and 1922. Further, front airflow aperture 1916B includes fingers 1926and 1930. When corresponding fans are inserted in these positions, thefingers will receive the flanges of corresponding fan housings.

The back surface 1912 includes a plurality of back airflow apertures1934A and 1934B that proximately limit backflow of air about the fanhousings that couple to the corresponding front airflow apertures. Forexample, back surface 1912 includes back airflow apertures 1934A and1934B that correspond to front airflow apertures 1916A and 1916B,respectively. When a fan matingly engages fingers, e.g., fingers 1918and 1922 corresponding to front airflow aperture 1916A, and the fanmoves against a bottom surface 1938, the back surface 1912 and, inparticular, the back airflow aperture 1934A, engages the housing of thecorresponding fan. In such case, this back airflow aperture 1934A limitsthe backflow of air about the sides of the fan.

FIG. 20 is a schematic side view of a multi-fan module constructedaccording to the present invention. FIG. 20 provides additional detailfrom a different view of the fan assembly according to the presentinvention. In particular, a front airflow aperture 1916A is open fromthe view of FIG. 20. In such case, a back airflow aperture 1934A isevident as is back airflow aperture 1934B corresponding to front airflowaperture 1916B. Fingers 1906 and 1904 corresponding to front airflowaperture 1918 are shown to be formed in a front edge 1908 of the fanassembly.

FIG. 21 is a schematic view of a prior art technique for couplingoptical fiber media to a printed circuit board. FIG. 21 illustrates acircuit board 2100. Mounted upon circuit board 2100 are a plurality ofoptical fiber couplers 2102A, 2102B, 2102C, and 2102D, each of whichreceives a pair of optical fiber media. As is shown, the optical fibermedia are received by the optical fiber couplers 2102A, 2102B, 2102C,and 2102D in a direction that is substantially perpendicular to a frontedge 2108 of the circuit board 2100. The front edge 2108 of the circuitboard 2100 is oriented such that when the circuit board 2100 is receivedwithin an opening, the front edge 2108 will be substantially parallel tothe housing opening through which the circuit board 2100 is received.

Thus, with this orientation, the optical fiber media 2104A, 2104B, 2106Aand 2106B are received within the optical fiber media coupler 2102 wellaway from the front edge 2108 of the integrated circuit board 2100. Suchis the case because sufficient distance must remain between the opticalfiber media couplers 2102A-2102D and the front edge 2108 of the circuitboard 2100 so that the optical fiber media may be directed and extendedfrom the housing in a direction substantially parallel to the front edge2108 of the circuit board 2100. However, because a minimum bend radiusis required so as not to damage the optical fiber media, the mediacouples 2102A-2102D must be set back a minimum distance from the frontedge 2108 of the circuit board 2100. In the prior art embodiment of FIG.21, therefore, the limitations involving the placement of the opticalfiber media coupler resulted in wasted space on the integrated circuitboard 2100.

FIG. 22 is a schematic view of a daughter board constructed according tothe present invention in which optical fiber media couples to thedaughter board substantially parallel to a front edge of the daughterboard. As shown in FIG. 22, a daughter board 2202 includes a faceplate2204 fixed to, and parallel with, a front edge of the daughter board2202. When engaged within the enclosure or another housing, the frontedge of the daughter board 2202 will be substantially parallel to asurface of the front panel of the enclosure.

Fixed to the daughter board 2202 is an optical fiber media coupler 2206.The optical fiber media is disposed parallel to the front edge of thedaughter board 2202 such that optical fiber media 2208 is received in adirection substantially parallel to a housing opening in which thedaughter board 2202 is installed.

The daughter board 2202 also includes optical fiber media guides 2210and 2212 installed on the daughter board 2202. The optical fiber mediaguide 2210 and 2212 each have a radius about which the optical fibermedia 2208 are routed so that the optical fiber media 2208 extend froman opening 2214 in a direction that is substantially parallel to thehousing opening. In this fashion, the optical fiber media. 2208 and 2210form a semi-circle with the minimum radius about the optical fiber mediaguide 2210. The radius of the optical fiber media guide 2210 is onewhich allows the media to be bent about the guide without damage.

Significantly, the daughter board 2202 may be constructed with a minimumdepth that is sufficient to contain the optical fiber media coupler2206. With the minimum depth, the daughter board 2202 uses a minimaldepth of the available depth within the housing for the requiredintegrated circuitry, i.e., the motherboard.

FIG. 23 is another view of a daughter board constructed according to thepresent invention showing the manner in which optical fiber mediacouples to the daughter board. As shown in FIG. 23, a daughter board2202 includes an optical-fiber media coupler 2302 that is mountedparallel to, but in an opposite direction, as compared to the opticalfiber media coupler 2206 of FIG. 22. The daughter board 2202 includesthe disposed optical fiber media guides 2210 and 2212 that were shown ondaughter board 2202 of FIG. 22.

In the structure shown in FIG. 23, the optical fiber media coupler 2302receives optical fiber media 2308. The optical fiber media 2308 isrouted about the second optical fiber media guide 2212 and also aboutthe optical fiber media guide 2210, such that the optical fiber media2308 extends through the opening 2214 in the same direction as opticalfiber media 2208 extends from the opening 2214 in FIG. 22.

FIG. 24 is a diagrammatic top view of a daughter board constructedaccording to the present invention showing the manner in which aplurality of optical fiber media couple to the daughter board. As shown,four optical fiber media couplers 2206, 2302, 2402, and 2404 are mountedupon a daughter board 2202. Optical fiber media 2208, 2308, 2408, and2412 (each of which includes two optical fiber cables) couple to opticalfiber media couplers 2206, 2302, 2402, and 2404, respectively.

As is shown, optical fiber media coupler 2206 couples to a to surface ofthe daughter board that receives optical fiber media 2208 in a firstdirection that is parallel to the front edge of the daughter board,Further, optical fiber media coupler 2402 also couples to the surface ofthe daughter board and receives optical fiber media 2408 in the firstdirection. Optical fiber media couplers 2302 and 2404 couple to thesurface of the circuit board and receive optical fiber media 2308 and2412, respectively, in a second direction that is substantially parallelto, but opposite, the first direction.

Optical fiber media guide 2212 couples to the surface of the daughterboard and tangentially receives optical fiber media 2308 and 2412.Optical fiber media guide 2212 provides a routing path for the opticalfiber media 2308 and 2412 in the manner shown. As illustrated, theoptical fiber media guide 2212 includes an opening 2406 through whichoptical fiber media 2308 and 2412 are received. Thus, the optical fibermedia guide 2212 provides different routing paths for optical fibermedia 2308 and optical fiber media 2412.

Optical fiber media guide 2210 also tangentially receives optical fibermedia 2308 and 2412 and provides a routing path for the optical fibermedia 2308 and 2412. Optical fiber media guide 2210 also tangentiallyreceives optical fiber media 2208 and 2408 and provides a routing pathfor the optical fiber media 2208 and 2408. In combination, the opticalfiber media guides 2210 and 2212 provide routing paths so that theoptical fiber media extend from the daughter board and a housing openingadjacent the front edge of the daughter board substantially parallel,and in the same direction to the front edge of the daughter board. Therouting paths provided prevent the optical fiber media 2208, 2308, 2408,and 2412 from being bent at a radius less than that provided by theoptical fiber media guides 2210 and 2304.

FIG. 25 is a logic diagram illustrating a method for inserting a faninto the multi-fan tray according to the present invention. The methodrequires first unlatching the multifan tray from an enclosure housingthe multifan tray (step 2502). Then, the multifan tray is removed fromthe enclosure (step 2504). Next, the power supply is disconnected from afailed fan of a plurality of fans held by the multifan tray (step 2506).The failed fan is extracted from the multifan tray by lifting the fan toremove a flange of the fan from a plurality of fingers formed in themultifan tray that slidingly engage the flange (step 2508).

With the failed fan removed, a new fan is inserted into the multifantray by engaging a flange of the fan into the plurality of fingersformed in the multifan tray (step 2510). The new fan is then connectedto the power supply (step 2512). Then, the multifan tray is insertedinto the enclosure (step 2514). Finally, the multifan tray is latchedinto the enclosure (step 2516).

FIG. 26 is a logic diagram illustrating a method installing an opticalfiber media onto a printed circuit board according to the presentinvention. According to this operation, an end of an optical fiber opticmedia is inserted into an optical fiber media coupler that resides in asubstantially parallel orientation relative to a front edge of theprinted circuit board (2602). Then, the optical fiber media is routedabout a radial surface of an optical fiber media guide (step 2604).Finally, the optical fiber media is extended through a media egressaperture in a substantially parallel direction with respect to the mediaegress aperture (step 2606). The media egress aperture is referred to as2214 in FIG. 22.

FIG. 27 is a logic diagram illustrating a method for constructing a cardguide according to the present invention. According to this method, apair of elongated guides are designed that affix to a circuit board andthat allow the circuit board to be slidingly engaged within anenclosure. Within the enclosure is produced a cooling airflow and theenclosure includes a pair of slots that receive the pair of elongatedguides. The method commences by determining a division of the coolingairflow volume within the enclosure by the location of the pair of slotassemblies (step 2702).

The method then proceeds with determining a first heating amountproduced by a first plurality of components residing upon a firstsurface of the circuit board (step 2704). Then, a second heating amountproduced by a second plurality of components residing upon a secondsurface of the circuit board is determined (step 2706). Finally, anoffset of second portions of the elongated guides from first portions ofthe elongated guides is determined to selectively divert a portion ofthe cooling airflow from one surface of the circuit board to an oppositesurface of the circuit board (step 2708). This method may be extended todesign offsets for a plurality of elongated guides for a systemcontaining a plurality of circuit boards.

The invention disclosed herein is susceptible to various modificationsand alternative forms. Specific embodiments therefore have been shown byway of example in the drawings and detailed description. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the claims.

What is claimed is:
 1. A rack-mountable system enclosure for limitingthe escape of internally-generated electromagnetic interference, thesystem enclosure comprising: a system case; a front panel; a back panel;overlapped seams formed to couple the front panel and the back panel tothe system case such that no gaskets and a minimal number of fastenersare required wherein fasteners includes welds, rivets and screws; atleast one front opening through which communication media passes;apertures formed within the system case for providing air inlet andegress ports; wherein the system enclosure defines a first volume thatreceives a cooling fan module a second volume that receives a pluralityof integrated circuit boards, and a third volume through which coolingair exits; the first volume is separated from the second volume by afirst divider having perforations formed therein to pass air flow fromthe first volume to the second volume, and the second volume isseparated from the first volume by a second divider having perforationsformed therein to pass airflow from the second volume to the thirdvolume.
 2. The rack-mountable system of claim 1, wherein: the systemcase is formed of a top panel and a bottom panel; and the top panel andthe bottom panel are joined via overlapped seams having no gaskets and aminimal number of welds.
 3. The rack-mountable system enclosure of claim1, wherein: the first divider is formed separate from the systemenclosure and the second divider is integrally formed with the systemenclosure.
 4. The rack-mountable system enclosure of claim 1, wherein:the system enclosure is formed of a top panel and a bottom panel, thetop panel and the bottom panel are joined via overlapped seams having nogaskets and a minimal number of fasteners; and the second divider formsa portion of the top panel.
 5. The rack-mountable system enclosure ofclaim 1, wherein: the system enclosure is formed of a top panel and abottom panel; the top panel and the bottom panel are joined viaoverlapped seams having no gaskets and a minimal number of fasteners;the first divider forms a portion of the top panel; and the seconddivider forms a portion of the top panel.
 6. The rack-mountable systemenclosure of claim 1, Further comprising; a first plurality of slotassembly assemblies affixed to the first divider, the first plurality ofslot assembly assemblies adapted to receive card guides; and a secondplurality of slot assemblies affixed to the second divider, the secondplurality of slot assemblies adapted to receive card guides.
 7. Arack-mountable communication system box that provides limited escape ofinternally generated electromagnetic interference, the system boxcomprising: a system case, a front panel; a back panel; overlapped scamsformed to couple the front panel and the back panel to the system casesuch that no gaskets and a minimal number of fasteners are requiredwherein fasteners includes welds rivets and screws; at least one frontopening through which communication media passes; a cooling fan module;a plurality of integrated circuit boards upon which integrated circuitryis mounted and to which communication media couples; least one backplane connector to which the plurality of circuit boards couples whereinthe system case defines a first volume that receives the cooling fanmodule, a second volume that receives the plurality of integratedcircuit boards, and a third volume through which cooling air exits;wherein the first volume is separated from the second volume by a firstdivider having perforations formed therein to pass air flow from thefirst volume to the second volume: and wherein the second volume isseparated from the first volume by a second divider having perforationsformed therein to pass airflow from the second volume to the thirdvolume.
 8. The rack-mountable communication system box of claim 7,wherein: the system case is formed of a top panel and a bottom panel;and the top panel and the bottom panel are joined via overlapped seamshaving no gaskets and a minimal number of fasteners.
 9. Therack-mountable communication system box of claim 7 wherein: the firstdivider is formed separate from the system case; and the second divideris integrally formed with the system case.
 10. The rack-mountablecommunication system box of claim 9, wherein: the system case is formedof a top panel and a bottom panel; the top panel and the bottom panelare joined via overlapped seams having no gaskets and a minimal numberof fasteners; and the second divider forms a portion of the top panel.11. The rack-mountable communication system box of claim 9, wherein: thesystem case is formed of a top panel and a bottom panel; the top paneland the bottom panel are joined via overlapped seams having no gasketsand a minimal number of fasteners; the first divider forms a portion ofthe top panel; and the second divider forms a portion of the top panel.12. The rack-mountable communication system box of claim 9, furthercomprising; a first plurality of slot assemblies affixed to the firstdivider, the first plurality of slot assemblies adapted to receive cardguides of the plurality of integrated circuit boards; and a secondplurality of slot assemblies affixed to the second divider, the secondplurality of slot assemblies adapted to receive card guides of theplurality of integrated circuit boards.
 13. The rack-mountablecommunication system box of claim 7, further comprising, for each of theplurality of integrated circuit boards, at least one front shieldingpanel.
 14. The rack-mountable communication system box of claim 7,wherein the cooling fan module includes at least one shielding surfaceto prevent the escape of electromagnetic interference from the systembox.
 15. A communication system switch comprising: a rack; a pluralityof system boxes mounted on the rack that provide limited escape ofinternally generated electromagnetic interference, each of the pluralityof system boxes comprising: a system case; a front panel; a back panel;overlapped seams formed to couple the front panel and the back panel tothe system case such that no gaskets and a minimal number of fastenersare required wherein fasteners includes welds, rivets and screws; atleast one front opening through which communication media passes;wherein the system case defines a first volume that receives a coolingfan module, a second volume that receives a plurality of integratedcircuit boards, and a third volume through which cooling air exits, thefirst volume is separated from the second volume by a first dividerhaving perforations formed therein to pass air flow from the firstvolume to the second volume; the second volume is separated from thefirst volume by a second divider having perforations formed therein topass airflow from the second volume to the third volume; a cooling fanmodule; a plurality of integrated circuit boards upon which integratedcircuitry is mounted and to which communication media couples; and atleast one back plane connector to which the plurality of circuit boardscouple; and communication coupling among the plurality of system boxes.